Wild Fermentation

A cluster of grapes is an all-inclusive wine starter kit – everything you need to make wine is pre-packed in each and every cluster: sugar, acid, yeast. This year, I wanted to make one batch of wine that simply let the grapes do their thing.

If you’ve ever seen grapes ripe on a vine, or bought some particularly fresh ones, you may have noticed a thin white film on each grape. This is called the ‘bloom,’ and you’ll find it on all sorts of fruits. Have you ever been apple picking, and seen the white powdery coating on a freshly plucked apple before you rubbed it on your flannel shirt to get it all shiny? Or noticed fingerprints on plums in a supermarket? That’s the bloom! In that bloom are wild yeasts, capable of turning grape juice into wine.

Concord grapes with a visible bloom.
The bloom is easy to see on these Concord grapes (which I did not turn into wine but did eat). Massachusetts, 2017

Conventional winemaking usually calls upon lab-grown yeasts to do the fermentation – these yeasts have been bred to live and die under certain conditions (temperature ranges, alcohol contents) and produce certain flavors (to help make a chardonnay taste like a chardonnay, for example). This all gives the winemaker a greater degree of control over the finished product. Winemaking friends, professionals, and manuals all advised me strongly against using the wild yeasts on the grapes to make wine, above all because of wild yeasts’ unpredictability.

My undergraduate years studying ancient history helped me to shrug off this advice. Think of the ancient Egyptians, Greeks, and Romans, the Georgians and Phoenicians: they all made wine using wild yeasts — for millennia. Why shouldn’t I?

Wild Fermented Wine: 2020 Method

Fermentation recap: grape juice becomes wine when yeasts eat the sugar in the juice and turn it into alcohol and CO2.

To give the yeasts living on the grape skins more time to get munching on the sugars in the grape juice, I didn’t separate the juice from the rest of the grape matter. Right after stomping the grapes, I scooped about 4 gallons of must into a fermentation bucket: juice, seeds, skins, pulp and all. I pulled out most of the stems by hand so they wouldn’t make the wine too tannic or grassy, but left everything else all together. Following the advice of wild fermenting youtubers, I stirred in a quarter cup of raw honey. This helped to boost the sugar content, and incorporated more wild yeasts that were living in the honey. I put this bucket in a cool, dark corner in my apartment and covered it with a hand towel, stirring the must about 5 times a day.

On the fourth day, when I pulled back the hand towel to stir, the must looked completely different. The grape skins were all pushed to the top and looked almost dry, and when I stirred the mixture, the juice frothed. I rejoiced – the fermentation had taken hold!

I kept stirring many times a day for a few more days, and then strained out the skins and seeds from the juice. I topped the bucket with an airtight seal (including an airlock to allow gases produced by the yeasts to safely escape).

Then a record-breaking heat wave hit San Francisco, and I was completely unprepared. Nearly every day I have lived in this city, the temperatures stay in the sixties, perhaps in the low seventies. I wear a turtleneck year-round; we don’t have AC, and never even thought to buy a fan. But climate change has changed everything, and it was 95 degrees in our apartment. My partner searched in vain for a fan for sale somewhere in the city as I lay on the floor with a cool washcloth on my forehead. The airlocks that had been burbling on my buckets of wine slowed to a standstill; this meant the yeasts had died, after only a week of fermentation, and two entire weeks early.

The heat had accelerated the yeasts’ work. Just like bread dough rises faster in a warm place, the wine yeasts plowed through the sugars more swiftly in warm temperatures. But faster is not better when it comes to wine. The yeasts were fermenting so furiously that the chemical and biological processes were getting wonky. When I opened the buckets, I smelled sulphur: a winemaker’s nightmare. I stirred the wine to release the sulphur, resealed the buckets, and wrapped them in wet t-shirts to try to keep the temperatures down through evaporative cooling.

The wild fermented wine stopped smelling of sulphur the next day, for which I was grateful, but the airlock remained still. The yeasts had perished, so I tasted the wine to see if they had turned all the sugar into alcohol or died before they got the chance.

The wine tasted brash, green, tannic, punchy, aggressive. This was not a smooth, buttery, canonical chardonnay. But the wine was dry – no sweetness remained. This meant the wild yeasts had completed the fermentation, even under the perilous conditions of San Francisco’s heat wave. I was impressed and fiercely proud of the the wild yeasts, which my friends, advisors, and winemaking texts had underestimated. The wild fermented wine actually survived the heat better than the conventional (lab-grown yeast) fermented wine; I believe this is because the wild fermentation began much more slowly.

After a week of resting the wild-fermented wine, I tasted it again. The flavors had significantly mellowed: though still a wine with plenty of personality, ‘brash’ was no longer the first word that came to mind with a sip. The wine had survived an extreme fermentation process, and I was ready to turn it into vermouth and get it in the bottle.

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